This present embodiments relate to manipulating contrast agents. For contrast agents with drugs, fragmentation of the contrast agents away from the tissue for treatment is generally not desired. Release of drugs in a center of a vessel may lead to the drugs not being applied to the desired vessel wall.
Acoustic radiation force is used to displace the contrast agents towards the tissue to be treated or into a greater concentration, but while minimizing destruction. Acoustic radiation force may improve the binding efficiency of targeted contrast agents, such as increasing a number of drug filled contrast agents that bind with a vessel wall, activated endothelium or other area.
Radiation force increases with greater resonance with the contrast agents. The displacement increases linearly with increasing pulse length. Greater resonance and long pulse length may be used for displacement while minimizing fragmentation. Fragmentation is weakly a function of pulse length, such as the contrast agent slowly shrinking due to the acoustic radiation force until the frequency of the force is low relative to the resonant size of the contrast agent. Fragmentation is more strongly a function of the mechanical index, or the peak negative pressure divided by the square root of the center frequency. Therefore, low mechanical index is used for generating radiation force without destroying the contrast agent.
Low mechanical index B-mode imaging of contrast agents may allow imaging of contrast agents while minimizing destruction. Pulsed waves are used for imaging. Contrast agents have been imaged in combination with application of therapeutic ultrasound energy. The imaging and therapy pulses are sequentially transmitted. The therapy pulses are used to increase a temperature and associated uptake characteristic of tissue for drug delivery.